Billy Gilmour has signed a four-year contract with the Seagulls.
The 21-year-old midfielder has penned a four-year contract with Brighton on the deadline day.
He has spent the last season on loan at Norwich City and has not made an appearance for the Blues this campaign.
Last summer, he extended his contract with Chelsea until 2024 but now leaves Stamford Bridge after making only 21 appearances for the Blues.
Chelsea will receive an initial £7.5m fee that could go up to £10m if certain conditions are met.
He has 15 caps for Scotland and was the standout player against England in the European Championships last year.
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“Billy arrives with a fantastic pedigree, having played in the Premier League and Champions League as well as for Scotland at last year’s Euros,” said Brighton manager Potter. “He will complement our existing midfield options.
“That experience at quite a young age shows the strength of character he has and we’re really excited by his potential.”